Heterocyclic N-halamine groups are known to have biocidal properties that can be put to use in water purification. Heterocyclic N-halamine groups that are attached to a polystyrene polymer are described in U.S. Pat. No. 5,490,983. A crosslinked polystyrene polymer having similar pendant heterocyclic N-halamine groups is described in U.S. Pat. No. 6,548,054. The crosslinked version of the polystyrene polymer is typically provided in beads that do not have the problems associated with a powder. The beads are available from Vanson HaloSource of Redmond, Wash. A representative heterocyclic amine group described in both of these patents is a hydantoin group. When the hydantoin group has a chlorine or bromine atom bonded to one or both of the hydantoin nitrogen atoms, the hydantoin is biocidal. Worley et al. '054 describe methods for the creation of the biocidal halogenated polystyrene hydantoin (HPSH) polymer from the non-biocidal polystyrene hydantoin (PSH) polymer using a variety of free chlorine sources (for example, sodium hypochlorite, calcium hypochlorite, sodium dichloroisocyanurate). Over time however, the biocidal HPSH polymer reverts to nonbiocidal PSH polymer as a result of depletion of the halogen atoms due to contact with the biodemand. PSH polymer, however, has the ability to be recharged or rehalogenated with a halogen to restore its antimicrobial properties.
Worley et al. '054 describe recharging PSH polymer once the polymer has lost its biocidal efficacy by halogenating the PSH polymer using concentrated solutions of industrial strength liquid bleach and bromine. It has been determined that the levels of halogen in solution according to Worley et al. '054 are of such high concentration that when used in-situ in a water treatment device, the subsequent purified water is rendered undrinkable and requires considerable post-treatment to remove the excess halogen to render the purified water drinkable.
One of the drawbacks of using HPSH polymer in water filters is that once the halogen is consumed from the HPSH polymer, the halogen must be either replaced by recharging the halogen-depleted PSH polymer, or the entire mass of PSH polymer must be discarded and replaced with fresh HPSH polymer. Until now, there was no practical alternative to either recharging or replacing the PSH polymer in a water treatment system. Replacing halogen-depleted PSH polymer with fresh HPSH polymer raises the capital and operating costs of the water treatment system. Recharging PSH polymer that has lost biocidal efficacy requires that the water treatment system be taken out of service. Off-line recharging of PSH polymer to HPSH polymer creates considerable down-time and system complexity.
Another short-coming of HPSH polymers is the drop in biocidal efficacy during use. As halogen is consumed from the HPSH polymer, the biocidal efficacy of the HPSH polymer drops below commonly required biocidal performance standards, such as the United States Environmental Protection Agency (EPA) purifier standards of 6 log removal of Klebsiella, and 4 log removal of poliovirus. While the drop in biocidal efficiency is expected as halogen is consumed by the biodemand, the speed at which this reduced effectiveness occurs creates several difficulties for the practical application of the HPSH polymer in applications, such as a water filter in the home or as an emergency water supply. Product designers and engineers wishing to apply HPSH polymer technology to commercial products must either increase the initial amount of HPSH polymer to achieve the desired performance life of the product or add complexity to the system by allowing for off-line rehalogenation of the PSH polymer.
Accordingly, there is a need to provide methods and the means to maintain constantly or for a prolonged period of time, a biocidally effective halogen charge on polymers having pendant heterocyclic N-halamine groups without adversely affecting water quality, and without the need to recharge or replace the halogen depleted PSH polymer. The present invention fulfills this need and has further related advantages.